Four-pole earphone device including left and right speaker terminals, microphone terminal and ground terminal includes first switch between the left and right speaker terminals to switch connection of the left and right speaker terminals; second switch between the right speaker terminal and control unit to switch connection of the right speaker terminal and the control unit; third switch between the right speaker terminal and microphone/key function unit to switch connection of the right speaker terminal and the microphone/key function unit; the control unit monitoring power from terminal equipment, controlling switching, of the first, second and third switches according to value of the power, and controlling the left and right speaker terminals, the microphone/key function unit and earphone output unit; and the microphone/key function unit connected to the microphone terminal and the control unit to perform microphone and key functions of the four-pole earphone device.